Elsevier

Social Science & Medicine

Volume 49, Issue 6, September 1999, Pages 763-779
Social Science & Medicine

The cost-effectiveness of introducing a varicella vaccine to the New Zealand immunisation schedule

https://doi.org/10.1016/S0277-9536(99)00115-XGet rights and content

Abstract

This study examined the cost-effectiveness of adding a varicella vaccine to an existing childhood immunisation schedule relative to a counterfactual where the varicella vaccine is available on a user-pays basis (the current New Zealand situation). The costs and consequences of chickenpox in an annual cohort of 57,200, 15-month old children were simulated for a 30-year period. The cohort simulation design captures the `phasing-in' effects of routine varicella vaccination on the population.

From a health care payer's perspective (medical costs only) every dollar invested in a vaccination programme would return NZ $0.67. However, from a societal point of view (which includes the value of work-loss), a vaccination programme would return NZ $2.79 for every dollar invested. To implement a varicella vaccination programme covering 80% of 15-month old children in New Zealand would add more than NZ $1 million in net direct (health care) costs each year. However, the indirect cost savings from reduced losses of work-time exceed NZ $2 million annually.

The net average health care cost per child vaccinated over the 30-year modelling period was $54 whereas the cost-savings from work-loss averted averaged $101 per child vaccinated. Total cost-savings to society of $47 per child vaccinated, on average, could be gained from a vaccination programme.

The finding that the addition to vaccination costs resulting from a routine programme (including the cost of complications from the vaccine) were greater than the offsetting health care cost savings from reduced incidence of chickenpox were robust to a sensitivity analysis on all assumptions within plausible ranges. Overall cost-effectiveness estimates were most sensitive to assumptions regarding lost work-time, the discount rate, and the price and efficacy of the vaccine. Estimates were relatively insensitive to changes in assumptions regarding health care utilisation.

Introduction

Chickenpox is an infectious disease caused by the varicella-zoster virus (VZV). The reported incidence of chickenpox varies, but most studies concur that at least 90% of the population will have contracted chickenpox by the age of 15 years Preblud, 1986, Finger et al., 1994, CDC, 1996. Based on this information, it is estimated that in New Zealand more than 50,000 cases of chickenpox occur annually. In addition, an average of 128 hospitalisations and 0.8 fatalities are associated with this disease annually (New Zealand Health Information Service, 1984-1995a, New Zealand Health Information Service, 1984-1995b).

A routine varicella vaccination programme targeted at healthy children can largely prevent the morbidity and mortality associated with the varicella virus. Overseas evidence also suggests that such a programme would be cost-effective. Lieu et al. (1994) found that a routine varicella vaccine would result in net savings from a societal perspective (where the consequences of the vaccine include work loss averted due to a reduced incidence of disease). From the more restrictive perspective of health care funders, the vaccine did not save money, but was judged to be relatively cost-effective compared to other prevention programs. Varicella vaccination was added to the US immunisation schedule in 1995, with a single injection given at 12–18 months of age. Broadly comparable results to those of Lieu et al. (1994) were found by Beutels et al. (1996) in their evaluation of a varicella vaccination for German children.

New Zealand does not currently include vaccination against chickenpox on the government financed childhood immunisation schedule. The varicella vaccine is, however, available and individuals can obtain it from their general practitioners on a user-pays basis at a cost in 1997 of around NZ $62 (excluding Goods and Services Tax). The varicella vaccine approved for use in New Zealand is the Varilrix™ vaccine, an Oka-strain live attenuated vaccine. Oka-strain vaccines have a history of use in the US, Britain, Switzerland, Korea and Japan.

The aim of this study is to examine the cost-effectiveness of adding the varicella vaccine to the existing childhood immunisation schedule (Option 1), relative to a counterfactual scenario where the varicella vaccine is available on a user-pays basis (Option 2: the current New Zealand situation). Option 1 would entail the varicella vaccine being fully subsidised and administered at the same time (but as a separate injection) as the current trivalent measles, mumps and rubella vaccine (MMR), and the quadvalent diphtheria, tetanus, pertussis and haemophilus influenzae type b (DTPH) vaccines. The MMR and DTPH vaccines are administered to children at approximately 15 months of age. Research is currently being undertaken on a vaccine which would combine the varicella vaccine with the MMR, but this is unlikely to be available for another two to three years (Wells, 1996).

The modelling approach used in this study is similar to that used by Lieu et al. (1994), which facilitates comparison with these leading US results. An innovation of this paper is the inclusion of the costs and effects of varicella vaccinations received and paid for `privately' in the absence of a routine vaccination programme. These have been incorporated for two reasons. First, if the existing coverage of varicella vaccination is not acknowledged, the incremental gain in coverage and resulting cost-effectiveness of a routine programme would be over-estimated. Second, the rationale for a fully-subsidised routine programme must rest upon observations regarding the extent to which the market, left to its own devices, fails to achieve socially optimal outcomes.

The costs of vaccination and of illness caused by the VZV under both Options 1 and 2 are considered from a social perspective and include both direct health care resource use and indirect costs associated with time off paid work to care for sick children. Results are also reported from the more restrictive perspective of health care funders.

Section snippets

Methods

The cost-effectiveness analysis is based on a modelling approach to the costs and consequences of Option 1 (routine vaccination) relative to Option 2 (the existing situation). The model was developed on an Excel spreadsheet (version 5.0, Microsoft). The analysis is conducted for a 30-year period following the introduction of a routine varicella vaccination programme. The 30-year period was chosen primarily because this facilitates comparison of these results with those of Lieu et al. (1994).

Results

The incidents averted, direct costs and indirect costs for the first 30 years of a varicella programme are given in Table 4.

A varicella vaccination programme over a 30-year period could avert 852,720 cases of chickenpox including 267,750 GP visits, 1668 hospitalisations, 2 cases of long-term disability from encephalitis and 12 deaths (undiscounted). In addition, 131,000, 10,000 and 2,553,000 days of work lost from uncomplicated cases (GP visits and no treatment), hospitalised cases (including

Discussion

Introducing a routine state funded vaccination programme will result in a windfall gain to those parents that were willing and able to pay for vaccination in the absence of a programme. Using our baseline assumptions, the (undiscounted) windfall to the 10% of parents that would purchase the vaccine in the absence of a routine programme would be $359,931 annually from the introduction of a routine programme. However, in the absence of a routine programme, parents who are able to pay for the

Acknowledgements

The authors are grateful to the Department of Economics, the Department of Preventive and Social Medicine, and the Injury Prevention Research Unit, University of Otago, and the Centre for Health Economics Research and Evaluation (CHERE), University of Sydney, for support and resources provided for this research; SmithKline Beecham for providing a grant-in-aid to facilitate the involvement of the first author, the Health Research Council for the summer studentship awarded to the fourth author,

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